University of Wisconsin-Madison research is helping state potato growers dramatically reduce the chemicals they use to manage what traditionally has been a pesticide-intensive crop.

The research should lead to further reductions in pesticide use, adoption of less toxic compounds, and greater reliance on cultural practices and biologically based methods to keep pest populations in check, say researchers in the College of Agricultural and Life Sciences.

Those advances will help keep Wisconsin growers economically competitive. The state ranked third in the nation in potato production last year when growers averaged 410 hundredweight per acre from the state”s 85,000 acres of potatoes.

“Growers in Wisconsin already use the most advanced pest management methods of growers in any state,” says entomologist Jeffrey Wyman. “Now we want to help them take pest management to a new level.”

The work has already begun to pay dividends.

“In 1999, growers were able to control early blight and late blight while applying less than half as much fungicide,” says Walt Stevenson, a plant pathologist. Growers sprayed as often as in the past but used much smaller amounts of fungicides in each application.

Growers reduced the fungicides they applied thanks in part to Stevenson”s research on Quadris, a new fungicide that is less toxic and used in much smaller amounts than previous compounds. Results from three year”s of Stevenson”s studies helped accelerate the U.S. Environmental Protection Agency evaluation Quadris, which it approved for use across the United States in 1999.

“Virtually every potato grower in the state used Quadris to some degree last year,” Stevenson says.

Although Quadris cost more than traditional pesticides, Stevenson”s research showed how growers could get improved blight control at almost the same cost as traditional fungicides, while applying much less. Stevenson believes that the improvement in blight control contributed to an average increase in potato yield across Wisconsin in 1999 of 40 hundredweight per acre. That increased yield was worth $17 million to Wisconsin growers.

In what resembles a regional game of hide-and-seek, growers in the Plover area are planning to avoid problems with the Colorado potato beetle by coordinating where each will plant the crop. Their decision follows a 3-year study by Deana Sexson, Wyman”s graduate student, who is also a Portage County Extension agent. Working in nearly 40 fields scattered across 45,000 acres, Sexson found that planting potatoes in fields a quarter mile or more from the previous year”s potato fields reduced beetle infestations by 85 percent.

Last summer, Wyman became the first researcher to show that parasitic wasps could control aphids successfully in commercial potatoes. “People promote predators like the green lacewing, but it”s a pin-head-sized parasitic wasp that can really keep the aphids in check,” he says.

Wyman used new, reduced-risk insecticides early in the growing season to control potato beetles while leaving the parasitic wasps in place. The wasps then kept aphids in check the rest of the season. Reduced-risk pesticides, which include Quadris, Fullfil and Spintor for potatoes, are compounds recognized by the EPA as less toxic to people and the environment than existing pesticides.

Twenty years ago, Wisconsin growers began adopting a set of tools that Stevenson, Wyman and other College researchers developed. Those tools allowed growers to predict pest outbreaks, reduce pesticide applications and minimize environmental contamination. The tools include professional pest scouting, monitoring weather conditions inside the crop canopy, and using computer software to predict outbreaks, set treatment thresholds, and adjust crop management.

“Initially the program improved disease control and reduced costs for growers,” says Stevenson. “But new strains of late blight appeared in the 1990s and growers had to increase sprays to combat the problem.”

The passage of the Food Quality Protection Act — which calls for the review and possible elimination of many chemicals now used on potatoes and other crops — prompted Stevenson, Wyman and their colleagues to rethink how Wisconsin growers could remain competitive in this changing regulatory environment.

“Our current methods have two weaknesses,” Wyman says. “First, we manage pests on a field-by-field basis. That”s not realistic because pests operate regionally. Secondly, we remain too dependent on pesticides. We react to pest outbreaks by killing pests where they appear, when we should be using biological control and cultural strategies to reduce pest populations before they become a problem.”

The goals of the new research effort include reducing the need for insecticides, using biological control where possible, replacing high-risk pesticides with reduced-risk alternatives, reducing the amount of pesticides applied, and minimizing the development of pesticide-resistant diseases and insects.

To reach these goals, the researchers must have much more information about pests and their enemies, both within individual fields and regionally. That means increased monitoring both of the pests and their enemies.

For example, there are three major insect pests in potatoes, according to Wyman. “We have to manage each while protecting and encouraging populations of beneficial organisms that can help control those pests,” he says. “And we need to do this not just in individual potato fields, but regionally with other crops and where crops aren”t grown.”

Last year, Wyman and Stevenson began evaluating new ways to improve pest management near Coloma, Wis. on 20 fields covering 2,500 acres. Three farms own the fields. The program monitored all pests on a five-acre grid in each field at weekly intervals. That level of pest scouting is twice as intensive as growers now use.

To maintain, analyze and display the information, the researchers turned to sophisticated computer and graphic systems. The systems transform the information on pests into maps that allow growers to view fluctuations in pest populations across the fields through time. This information greatly enhances the ability of growers to predict pest problems and deal with them effectively if they arise.

In a major experiment, Stevenson and Wyman also are evaluating three low-risk treatments and two conventional treatments for managing pests. The low-risk treatments include reduced-risk pesticides and use of biological controls where possible. The early results are encouraging, but the low-risk treatments cost more than conventional methods.

During the first two years, the researchers have found little difference in potato yields among the three low-risk and two conventional treatments. However, growing potatoes in this environmentally friendly way comes at a cost that level or slightly increasing yields may not offset, according to Wyman. Reduced-risk pesticides tend to be more expensive than conventional pesticides and the increased scouting also adds to the cost.

The researchers hope the type of information they”re collecting on the Coloma farms will enable them to predict times when the scouting schedule can be relaxed, thereby reducing the cost of the low-risk treatments. They also hope that consumers may be willing to pay slightly more for potatoes grown in an environmentally friendly way.

These studies have been supported by state funding to the UW-Madison College of Agricultural and Life Sciences and the UW-Extension Cooperative Extension Service. The research was supported by grants from the Wisconsin Potato and Vegetable Growers Association, the UW-Madison Pesticide Use and Risk Reduction program, and UW-Madison University-Industry Relations program; and by federal grants obtained in collaboration with the World Wildlife Fund from USDA-CSREES and EPA Pest Management and Environmental Stewardship programs.